1. Field of the Invention
The present invention relates to a dual band coupler and, in particular, to an improvement in design freedom of a dual band coupler, in which coupling coefficients of two main signal lines can be independently controlled.
2. Description of the Prior Art
Generally, A coupler used in a mobile telecommunication terminal device transmits a signal at a constant output through an antenna by distributing a transmitting signal in a proper ratio, or by taking a constant output signal from an amplifier of a transmitter and transmitting the signal to a automatic phase controller (APC).
With the need for multi-functional and small-sized mobile telecommunication terminal devices, dual band or triple band terminals are widely spread, which are characterized by the simultaneous service of two or more frequencies in one device. Accordingly, there is a strong demand for parts that can treat two different frequency bands. In response to such demand, dual band couplers have been developed.
In order to better understand the background of the invention, a detailed description will be given of a conventional dual band coupler in conjunction with drawings, below.
FIG. 1 is an equivalent circuit of a conventional dual band coupler. With reference to FIG. 1, the dual band coupler comprises a first main signal line 2 and a second main signal line 3 connected to an output amplifier of a transmitter treating different frequency band signals, and a coupling signal line 4 taking a predetermined amount of signal and adjacent to the first and second main signal line. The first and second main signal line 2 and 3 are provided with input IN1 and IN2 and output OUT1 and OUT2 terminals, and the coupling signal line 4 takes samples of input signals from different positions of the first and second main signal line 2 and 3 and transmits them to the automatic phase controller.
The dual band coupler forms a multiple layer type coupler consisting of multiple dielectric layers in order to provide a small-sized coupler.
FIG. 2 is an exploded perspective view of the conventional dual band coupler. Referring to FIG. 2, the dual band coupler comprises a first and fifth dielectric layer 11 and 15 having ground patterns 21 and 25; a second and third dielectric layer 12 and 13 having the first and second main signal lines 22a and 22b, 23a and 23b; and a fourth dielectric layer 14 having coupling signal lines 24a and 24c. The second and third dielectric layers 12 and 13 comprise two laminated dielectric layers 12a and 12b, 13a and 13b, and electrode patterns formed on dielectric layers, i.e. signal lines 22a and 22b, 23a and 23b, are connected to each other through conductive via-holes h1 and h2. Furthermore, the fourth dielectric layer 14 consists of two laminated dielectric layers 14a and 14b, and signal lines 24a, 24b, and 24c formed on the dielectric layers 14a and 14b are connected to each other through conductive via-holes h3 and h4. In addition, both ends of signal lines connected to each other through via-holes are extended to edges of dielectric layers to be connected to a lateral terminal, which will be formed in a subsequent process.
However, conductive patterns constituting signal lines should be formed at different positions on dielectric layers in order to shield mutual electromagnetic interference between the first and second main signal lines. Therefore, an area, in which the signal line is formed, becomes relatively small, and so precision patterning is needed. As a result, production cost and rejection rate are increased.
Additionally, in a conventional dual band coupler of FIG. 2, it is hard to independently control coupling coefficients of the first 22 and second 23 main signal line. In a multiple layers type coupler, the coupling coefficient is defined as a thickness of the dielectric layer inserted between main signal lines and an inductance owing to a signal line pattern.
As described above, however, the dual band coupler does limitedly form the signal line pattern, and so the coupling coefficient cannot be desirably controlled. Also, in case of controlling the thickness of the dielectric layer, when the thickness t of the dielectric layer 14a of the fourth dielectric layer is controlled in order to control the coupling coefficient of the second main signal line 23, thicknesses of dielectric layers of the first main signal line 22 and the coupling signal line 24 are also varied. Therefore, the coupling coefficient of the first main signal line 22 is considered, thereby, it is very difficult to design the desired dual band coupler having various coupling coefficients required in mobile telecommunication terminal devices.
Therefore, there remains a need for a dual band coupler, which can independently control a coupling coefficient of the first and second main signal line.
Therefore, the primary object of the present invention is to overcome the above disadvantages encountered in prior arts, and to provide a dual band coupler, which can independently control a coupling coefficient of a first and second signal line by laminating a dielectric layer having a coupling signal line between dielectric layers having a first and second main signal line so that dielectric layers between the coupling signal line and main signal lines have a different thickness from each other, or by laminating different numbers of dielectric layers between the coupling signal line and main signal lines, respectively.
Another object of the present invention is to provide a dual band coupler, which has an improved isolation by forming a shielding pattern for excluding mutual electromagnetic interference between the first and second main signal line on the dielectric layer having the coupling signal line.
Based on the present invention, the above objects can be accomplished by a provision of a dual band coupler, comprising: a first ground pattern formed on a first dielectric layer; a first main signal line having a first input and output terminal, which is a conductive pattern formed on a second dielectric layer laminated on the first dielectric layer; a coupling signal line having a coupling terminal and an isolation terminal, which is a conductive pattern formed on a third dielectric layer laminated on the second dielectric layer; a second main signal line having a second input and output terminal, which is a conductive pattern formed on a fourth dielectric layer laminated on the third dielectric layer; and a second ground pattern formed on a fifth dielectric layer laminated on the fourth dielectric layer.
According to an embodiment of the present invention, a dielectric layer between the first main signal line and the coupling signal line is made to be different in thickness from a dielectric layer between the second main signal line and the coupling signal line, or dielectric layers between the coupling signal line and the first main signal line are different in number from the dielectric layers between the coupling signal line and the second main signal line, whereby the coupling coefficient of each main signal line can be independently controlled.
According to another embodiment of the present invention, an isolation between the first and second main signal line can be improved by providing a dual band coupler further comprising a shielding pattern for excluding electromagnetic interference between the first and second main signal lines. The shielding pattern is formed around the coupling signal line on the third dielectric layer so as to be separated from the coupling signal line.
According to another embodiment of the present invention, the second, third, and fourth dielectric layers may consist of plural layers. Particularly, when the third dielectric layer comprises plural layers, the third dielectric layer comprises three or more layers consisting of a first layer having the coupling terminal, on which the first conductive pattern is formed; a second layer having the isolation terminal, on which the second conductive pattern is formed; and a third layer formed between the first and second layer, on which the third conductive pattern connecting the first conductive pattern to the second conductive pattern is formed. The first, second, and third conductive patterns are connected to each other through via-holes. It is preferable that the shielding pattern is formed around the third conductive pattern on the third layer so as to be separated from the third conductive pattern. The reason is that coupling signal lines on dielectric layers having the coupling terminal and the isolation terminal are extended to edges of dielectric layers, and so the shielding pattern is hard to surround the third conductive pattern. When the shielding pattern does not surround the third conductive pattern, a shielding effect may be reduced. In addition, the shielding pattern comprises two ground terminals.
Furthermore, a small-sized dual band coupler may be obtained by omitting dielectric layers having only the ground pattern. The dual band coupler comprises the first main signal line having the first input and output terminal, formed on the first dielectric layer; the coupling signal line having the combined output terminal and the isolation output terminal, formed on the second dielectric layer laminated on the first dielectric layer; and the second main signal line having the second input and output terminal, formed on the third dielectric layer laminated on the second dielectric layer. The dual band coupler has the ground pattern formed on the second dielectric layer so as to be separated from the coupling signal line. The ground pattern shields electromagnetic interference between the first and second main signal line.
When the third dielectric layer consists of plural dielectric layers, it is preferable that the ground pattern is formed on the dielectric layer having only the coupling signal line without the isolation and coupling terminal.